Reliability of immunoradiometric assays for sex hormone binding globulin, androstenedione, 17-β estradiol and tumor markers CEA and CA15.3 to assess the biological response of megestrol acetate treatment in patients with advanced breast cancer

This study evaluated the effect of megestrol acetate administration on the serological assessment of some sex steroid hormones in women with advanced hormone-sensitive breast cancer. The serum levels of l7-β estradiol, androstenedione and sex hormone binding globulin (SHBG) were measured by means of radioimmunometric assays, before and during drug administration. A significant suppressive effect on SHBG and androstenedione levels in comparison with the baseline values was reached in 100% (40/40) and 51% (20/39) of patients, respectively, after two months of therapy; by contrast, 17-β estradiol levels showed an increase above the baseline levels in 18 out of 22 patients. These findings might be explained on the basis of a possible interference in vivo of megestrol acetate metabolites particularly in the estradiol assay, since a direct influence of the solubilized megestrol acetate was not observed in vitro. The hormone levels generally did not show any relationship with the course of the disease, so their serial determinations do not seem to be useful to assess the clinical status or evaluate response to therapy. In our group of patients, CEA and CA15.3 serum determinations were also carried out to monitor the efficacy of treatment. CEA and CA15.3 levels reflected the course of the disease in 58.9% (23/39) and 65.8% (25/38) of patients, respectively. The two tumor markers displayed a similar sensitivity in detecting cancer progression (64% CEA and 63% CA15.3), but CA15.3 seemed to have a better diagnostic value in evaluating the response to therapy and signalling tumor relapse.